The British quartet of Christian Malcolm, Craig Pickering, Marlon Devonish and Mark Lewis-Francis were second fastest in their heat in 38.33, behind Brazil - but that time was only good enough for them to qualify fifth fastest overall.

Jamaica, led home by Asafa Powell, set a world-leading time of 38.02, while the Americans, even without double sprint champion Tyson Gay, looked dangerous as they set a season's best mark of 38.10.

Devonish said: "It was very comfortable, we didn't do anything stupid and now we can just try and take care of business in the final."

But Malcolm added: "We are pretty confident, but it's not going to be easy."

Jeremy Wariner went into the 400m as an almost unstoppable force but he was toe-to-toe with Merritt off the final bend, before pulling away to run the last 100m clear.

The 23-year-old Texan edged closer to his mentor Michael Johnson's world record of 43.18 but could not quite find the final kick in Japan, though he did become the only other athlete apart from Johnson to win back-to-back world crowns.

"Next year it is to defend my Olympic title," Wariner said, "The world record, it will come when it should come."

American Allyson Felix made the defence of her 200m title look incredibly easy as she pulled clear of the field to win gold by over half a second in 21.81.

Felix, the youngest athlete to claim a sprint world title as a 19-year-old in Helsinki two years ago, matched Jamaican Marlene Ottey in winning back-to-back world championship 200m golds.

Xiang is now China's first male world champion on the track

Jamaica's Veronica Campbell, who had been chasing the sprint double in Osaka, took silver while Sri Lanka's 31-year-old Susanthika Jayasinghe finished strongly to snatch bronze.

"I've been waiting for so long to run under 22 seconds. It has not been an easy road, but finally I managed it," said Felix.

Liu Xiang set himself up nicely for the 2008 Beijing Olympics, where he will undoubtedly be the pin-up of the Games, by winning his first world title with a dominant hurdling display.

The 24-year-old Olympic champion surged clear of American duo Terrence Trammell and David Payne with three barriers to go to win in 12.95.

Payne's bronze came even though he only arrived in Osaka on Tuesday as a late replacement in the US team.

Defending decathlon champion Bryan Clay pulled out of the championships after sustaining an injury in his third event.

The American, who had been in second place after strong performances in the 100m and long jump, pulled his right quadricep muscle during the high jump, his manager Paul Doyle confirmed.

As soon as I hit the front I was running scared and these guys can smell that on you